I have seen a few questions now that have been asking for a recommendation for things like an app or a resource. For example, https://health.stackexchange.com/questions/1520/cross-platform-pedometer-apps-with-open-apis is asking for an app recommendation. It is a low quality question, but should other questions like this be on-topic? There is Software Recommendations SE where they would accept these types of questions if they have enough information.
Another type of question that I have seen asking for a recommendation are those asking for a resource for research or something similar. An example of this is https://health.stackexchange.com/questions/1523/brain-wave-research, which is asking for resources to help the OP learn about the effects of depression on brainwaves (though this specific question may be a better fit on Cognitive Sciences SE). Though this is a little bit different than the questions that ask for an app or something similar, it is still asking for a recommendation. The problem with this is that there isn't an SE site that will always take these questions.
So, should all questions asking for recommendations be on-topic? Or should certain types of recommendations be on-topic while others are not (ie: asking for resource - on-topic; asking for app recommendation - off-topic)?